Technical Field
This disclosure relates to integrated circuit devices, and more specifically, to matching of a bipolar transistor pair through electrical stress.
Background of the Related Art
In modern integrated circuitry in semiconductor chips, there are many circuits which depend upon a matched pair of transistors. Matched transistor pairs are utilized in differential and instrumentation amplifiers, logarithmic amplifiers and comparators. Another type of circuit using matched transistor pairs is a class of circuit called a current mirror. A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading.
Current mirrors using bipolar junction transistors, or more commonly bipolar transistors, depend on accurate matching of the characteristics of the bipolar pair used in the circuit. One of the more important characteristics is Vbe. Vbe is the voltage that falls between the base and emitter of a bipolar transistor. One example of a mirror circuit using matched bipolar transistors is a Wilson current mirror. A Wilson current mirror is a three-terminal circuit that accepts an input current at the input terminal and provides a “mirrored” current source or sink output at the output terminal.
Due to manufacturing tolerances, the bipolar transistors possess a variation in Vbe and other characteristics. To achieve good current mirroring, the Vbe of both transistors should be matched within a certain accuracy. In the prior art, to compensate for transistor mismatch, circuits usually use an electrical compensation or tuning method to match the currents of the two bipolar transistors used in a mirror. These methods use some sort of electrical circuit to compensate for the Vbe mismatch.